The role of fenestration in acute canine thoracolumbar intervertebral disc extrusion: Part 2-The biological and biomechanical effects of fenestration.

BACKGROUND: Prophylactic fenestration is widely performed to prevent recurrence of canine acute thoracolumbar intervertebral disc extrusion (IVDE); however, there is a paucity of specific data regarding the biological and biomechanical effect of this procedure on the intervertebral disc and vertebral column. AIM: To evaluate the biological and biomechanical effect of fenestration by synthesizing data from clinical canine literature and preclinical in vivo and ex vivo (rabbit) models, to provide relevant translational information for the canine scenario. CONCLUSIONS: Biologically, experimental models and limited canine literature demonstrate that fenestration initiates a robust reparative response characterized by rapid annular fibrosis, endplate sclerosis, and eventual ankylosis rather than a return to normal disc architecture. Biomechanically, while ex vivo studies demonstrate that fenestration causes acute segmental destabilization and laxity, in vivo models reveal that the biological healing process overrides this, resulting in profound segmental stiffness and significantly reduced range of motion over time. IMPLICATIONS: Although not yet directly demonstrated in clinical canine thoracolumbar IVDE populations, these translational findings from experimental models and limited canine data suggest that fenestration-induced ankylosis may alter spinal loading dynamics, potentially transferring mechanical stress to adjacent, non-fenestrated discs. This biomechanical shift highlights a clinical trade-off between the prophylactic benefit of the procedure and the long-term biological costs to the vertebral column. Consequently, more consideration is needed regarding the biological and biomechanical effects of fenestration in dogs, and more research is needed to determine the optimal extent of fenestration to minimize these deleterious sequelae.